It might be worth pointing out that I have t-shirt from O'Reilly, who are often cited as a canonical source, which has "PERL" on it - the same as the one on the right here. So whilst I do largely agree with merlyn it's not surprising there is some confusion.

I could argue that this is a typographic freedom, much the same way as I might write "Re-elect JOHN DENVER!" for emphasis or as part of a headline. I don't know anyone in the proper writing game at O'Reilly that doesn't spell it as the FAQ says to spell it.